If it’s truly just a 100GB hard drive, and it’s really working on high-speed settings, then such long recovery can only be explained by potential hardware issues with the hard drive OR the USB port it’s connected to. It’s also possible that another program is working with the disk at the same time. Finally, are you recovering to the same drive you are scanning?

We would estimate the Deep Scan session to be finished in 6-8 hours. It’s possible there’s an issue with recovering from external USB drive to another external drive. Can you try recovering to the main hard drive of your Mac? Try recovering at least a small portion of files to see if it’s faster. Also, it should help if you could try connecting this disk to the other USB port, and/or via a different USB cable. On our end, we are testing this same scenario in the lab to see what can cause the slowdown.